1. Field of the Invention
The invention relates to a hard disk drive device, and a fluid dynamic bearing spindle motor that can be designed small and thin, and an assembling method thereof.
2. Description of the Related Art
Desktop or notebook personal computers are currently the main application of hard disk drive devices. Depending on the future market trend, however, hard disk drive devices may be employed in small portable electronic devices such as mobile phones, card memories and the like. There will then be a high demand for small, thin, and low-cost hard disk drive devices.
FIG. 5 shows one conventional hard disk drive device. The case 51 includes a cylindrical boss 52 and an annular recess 53 around the boss 52 for accommodating a motor. The lower end of a cylindrical sleeve 54 fits in the cylindrical boss 52. The sleeve 54 accommodates a shaft 55 inside, with a radial bearing 56 provided therebetween. A large diameter hole 57 is formed in the lower end of the sleeve 54, which is tightly closed by a plate 58. The shaft 55 includes a flange 59 at the lower end, which is accommodated inside the large diameter hole 57 such as to be rotatable. Thrust bearings 60 are provided between the upper face of the flange 59 and the opposing stepped surface of the hole 57 and between the lower face of the flange 59 and the opposing plate 58.
The radial bearing 56 and the thrust bearings 60 are hydrodynamic bearings with surfaces having hydrodynamic pressure generating grooved. Oil or a lubricating fluid is filled in the small continuous clearance extending from the radial bearing 56 to the thrust bearings 60. In the upper part of the radial bearing 56 is formed a tapered surface where the inside diameter of the shaft 55 decreases upwards to form a tapered seal part 61. The oil surface is positioned in this seal part 61 so as to prevent oil leakage by surface tension.
The top of the shaft 55 protrudes from the top of the sleeve 54, and to this protruded part is fixedly attached the center of a generally hat-shaped hub 62. A hard disk (not shown) is fixedly mounted on an outer peripheral flange 63 protruding from the bottom on the outside of the hub 62. An annular rotor 64 of a motor 66 is fixedly attached below the outer peripheral flange 63, while a stator 65 is fixedly attached on the outer periphery of the cylindrical boss 52.
FIG. 6 shows another conventional hard disk drive device (see Japanese Patent Laid-Open Publication No. 2003-97546). The case 71 has a recess 72 for accommodating a motor. A base member 73 is fixedly fitted in the center of the recess. The base member 73 has an L-shape cross section with a protruding part 73a at the outer periphery. A flange 73b extends to the outside from the top of the protruding part 73a. A shaft 74 stands in the center of the base member 73. A bottomed cylindrical hub 75, or a cylindrical sleeve with a thrust plate 76 for closing its top end, is coupled from above onto the shaft 74.
A radial bearing 77 is provided between the shaft 74 and the hub 75. A thrust bearing 78 is provided between the bottom face of the hub 75 and the base member 73. A hydrostatic thrust bearing 79 is provided between the top face of the shaft 74 and the thrust plate 76. The hub 75 has a small diameter part at the bottom and a taper is formed on its outer surface such that the diameter decreases upwards. This tapered surface and the inner periphery of the protruded part 73a of the base member 73 form a tapered seal part 80, in which the oil surface is positioned so as to prevent oil leakage by surface tension. A retention ring 81 is fixed to the bottom at the outer periphery of the hub 75. The ring has an L-shape cross section and engages with the flange 73b for preventing the hub 75 from slipping out.
An annular rotor 82 of a motor 84 is fixedly attached around the lower part of the hub 75, while a stator 83 is fixedly mounted in the outer peripheral part of the recess 72.
FIG. 7 shows yet another conventional hard disk drive device (see Japanese Patent Laid-Open Publication No. 2003-35311). The case 91 has a recess 92 for accommodating a motor, and a truncated conical shaft 93 is fixedly fitted in the center of the recess 92. A permanent magnet 94 is disposed in the upper central part of the shaft 93 such that its position is adjustable. An inverted cup-shaped hub 95 is coupled on the truncated conical shaft 93, and a conical hydrodynamic air bearing 96 is formed between the shaft 93 and the hub 95.
An annular rotor 97 of a motor 99 is fixedly attached around the lower part of the hub 95, while a stator 98 is fixedly mounted in the outer peripheral part of the recess 92.
In the configuration shown in FIG. 5, the shaft 55 has the flange 59 at one end and the seal part 61 at the other end, the sleeve 54 is fitted on the shaft 55, and the hub 62 is mounted on the sleeve 54. Because of this complicated structure, the device has large dimensions both in the axial and radial directions of the shaft 55, making size, thickness, and cost reduction impossible.
With the configuration disclosed in Japanese Patent Laid-Open Publication No. 2003-97546 shown in FIG. 6, the hub 75 is directly fitted onto the shaft 74 to serve as a sleeve for the radial bearing 77 and the thrust bearing 78 between the bottom face of the hub 75 and the base member 73. However, the outer peripheral retention ring 81 at the bottom of the hub 75 for retaining the hub 75 is the cause of the large diameter of the hub 75 and an obstacle to reducing the size. The provision of the base member 73 which is separate from the case 71 and the retention ring 81 increases the number of components and makes the configuration complex. The difficulty in achieving sufficient assembling precision makes size and cost reduction impossible.
With the configuration disclosed in Japanese Patent Laid-Open Publication No. 2003-35311 shown in FIG. 7, because the hub 95 is supported by the hydrodynamic air bearing 96, the conical shaft 93 needs to have a diameter that is large enough to achieve necessary bearing rigidity, which imposes a limitation on the extent of size reduction. One possible solution would be to employ an oil bearing instead of the air bearing, but in that case, a reliable seal part for preventing oil leakage is necessary. However, the mere substitution of oil for air as the lubricating fluid would not lead to size, thickness, and cost reduction of the device since there is no indication, nor suggestion, in this publication as to a specific configuration for a simple seal part that can be formed without increasing the number of components.